The technical field of this invention is rear steering for a motor vehicle.
Almost all motor vehicles have steering apparatus controlling the front steer angle (the steer angle of the front wheels) of the vehicle to determine the desired direction of vehicle travel. It is also known in the prior art of publications, although physical examples are still rare, to provide supplemental rear wheel steer to provide oversteer assist of low speed vehicle maneuvers such as parking and/or high speed understeer to assist vehicle directional stability. One such system is responsive to vehicle speed to provide an out of phase rear steer angle at low speeds and an in phase rear steer angle at high speeds, with the magnitude of the angle being derived from the front steer angle in an open loop algorithm. But it is not easy to provide optimal control of rear steer angle in a middle range of vehicle speed with such a control.
The invention described and claimed herein relates to a rear steer control for a motor vehicle that considers vehicle velocity in three ranges and provides an out of phase rear steer angle in open loop control within a low velocity range for oversteer assistance of parking and similar vehicle maneuvers, an in phase rear steer angle in closed loop control responsive to vehicle yaw rate within a high velocity range for understeer vehicle stability assistance and a steer angle in closed loop control responsive to vehicle yaw rate within an intermediate velocity range. In a preferred embodiment, the closed loop control in the high velocity range may be combined with an open loop control. The control optionally provides supplemental throttle adjustments in coordination with the rear steer control for increased traction and stability in a turn.